I just can't stand that American thing of missing the H off a word (to sound French?), so you get the awful erbal (and not in the Rasta sense) for herbal. I've even heard uman for human, I mean what the fuck?
Yeahyeahyeah, it's pedantic and pointless. But it Does My Head In (should be in the other thread, clearly).
Edit: I guess if you're not pronouncing the H, "an [h]istoric..." is fine, but in Britain you sometimes hear it with the H pronounced, which sounds very ugly indeed. You wouldn't ask for "an half" of something or talk about "an house" record, would you?